Plural frequency signal generator

Abstract

For the purpose of generating oscillations having a plurality of different frequencies, a read-only memory stores a plurality of binary words which are read cyclically. The individual pulse signals supplied by the read-only memory, each such signal representing a succession of corresponding bits read from the read-only memory, are used to control latches and the required oscillations are obtained by filtering pulse signals supplied by the latches. To guard against equipment failure, the read-only memory and latches are duplicated, the pulse signals supplied by the two sets of latches being combined by means of gates before filtering.

We claim: 
     
       1. Apparatus for generating a plurality of electric signals, said apparatus comprising: (A) a read-only-memory having storage locations for a plurality of digital words,   (B) means cyclically to address said storage locations to cause each digital word to be read out in turn, and   (C) a plurality of means each responding to a corresponding different digit of the digital words read from the memory to derive respective electric pulse signals each of which have different fundamental frequencies.   
     
     
       2. Apparatus according to claim 1 wherein each of said plurality of means comprises a latch which periodically takes up a state depending upon the controlling digit value at that time. 
     
     
       3. Apparatus according to claim 1 wherein said read-only memory also supplies a parity checking signal as a result of being addressed as aforesaid, the parity checking signal being utilised to detect incorrect operation of the apparatus. 
     
     
       4. Apparatus according to claim 1 wherein there are also provided filters respectively to select oscillations having different frequencies from the pulse signals supplied by said plurality of means. 
     
     
       5. A signal generating system comprising two sets of apparatus each as specified in claim 1, means to ensure that the two sets run in synchronism and gating means to combine the corresponding signals supplied by the two sets, the arrangement providing for continued operation of the system in the event of equipment failure by either set of apparatus. 
     
     
       6. A system according to claim 5 wherein the gating means comprises a plurality of `OR` gates, each of these `OR` gates being arranged in the absence of equipment failure to combine corresponding signals supplied respectively by the two sets of apparatus. 
     
     
       7. A system according to claim 5 also including a plurality of filters arranged respectively to select oscillations having different frequencies from the pulse signals supplied by the gating means. 
     
     
       8. A system according to claim 5, wherein the means to ensure that the two sets run in synchronism operate in a master and slave relationship and is arranged so that selectively either one of the two sets may be the master set. 
     
     
       9. A method of generating a plurality of electric signals of the kind in which the signals have different periodically recurring waveforms, said method comprising the steps of: (A) storing a respective multi-digit number in each of a plurality of locations of a read-only-memory,   (B) cyclically addressing the read-only-memory to cause each of the multi-digit numbers to be read out in turn, and   (C) individually processing each digit of the multi-digit numbers so read out to obtain a respective electric signal for each of the digits,   (D) each of the electric signals having a respective different periodically recurring waveform related to the numerical values of the respective series of digits from which it is derived.   
     
     
       10. A method according to claim 9 comprising the additional step of filtering the electric signals supplied derived from the multi-digit numbers to obtain a plurality of oscillations having a sine wave form. 
     
     
       11. A method according to claim 9 wherein each multi-digit number stored in the read-only-memory is a binary number.